1. Technical Field of the Invention
The present invention relates to a method of transmission within a radio communication unit comprising two processors linked together by a connection internal to the radio communication unit.
2. Description of Related Art
The expression “radio communication unit” is understood to mean a device capable of exchanging data with other devices equipped with radio sending and receiving means compatible with those of said unit. Such a unit may, for example, be a computing unit, a games console, a keyboard, a display screen, a printer, a home automation appliance, a communication terminal, etc. Each of these units contains at least one package program or application, making it possible in particular for this unit to fulfill its main function, namely data processing in respect of a computing unit or a games console, data entry in respect of a keyboard, data display in respect of a screen, printing in respect of a printer, etc.
It is often advantageous to apportion, within the communication unit, the functions executed by this unit between two processors linked together by an internal connection.
The first processor may be specially adapted to the main function of the unit. To do this, it may comprise means specifically appropriate for the execution of the application corresponding to this function, such as particular memory elements or a specific controller of interfaces for entering inputs and/or for presenting data to a user of the unit.
The second processor may execute operations, so-called low-level operations, necessary for transmitting the data between this radio communication unit and an outside device. In addition to the control of a radio transceiver, it configures the data in a form adapted to their transmission by radio, such as, for example, an apportioning of the data into successively transmitted packets. Conversely, it groups together data of packets received successively by radio, which correspond to one and the same communication session.
Such a second processor may be of a model common to all the communication units that use one and the same mode of radio transmission. This results in a reduction in the cost of the second processor, through a scale effect during its manufacture. On the other hand, this second processor may be associated in one and the same unit with a first processor of a model that varies as a function of the main application intended to be executed in this unit. A specialization of each communication unit is thus obtained, while benefiting from the cost reduction related to a single model of second processor.
Such a radio communication unit structure, having two processors linked together by an internal connection, is considered herein below.
The radio signals sent or received by the unit cause interference of electromagnetic nature which may disturb the transmissions performed via the internal connection between the two processors. Transmission errors then appear during the deciphering of the codes transmitted via the internal connection.
Interference of other origins may also disturb the transmission of the codes between the two processors, such as, in particular, electric microdischarges arising at the level of the internal connection. A particularly low “signal-to-noise” ratio may consequently be observed on the internal connection.
For a unit powered by an autonomous energy source, of cells or batteries type, it is known to momentarily interrupt operation of one of the two processors so as to reduce the energy consumption of the unit. This processor resumes its operation only when it is invoked, in particular when it receives codes via the internal connection originating from the other processor. This resumption of operation often requires a rebooting time interval, even a short one, during which codes received via the internal connection may be lost or spoilt by errors.
Errors of transmission between the two processors give rise subsequently to defective operations executed by the application or communication faults between the units linked by radio.
Several modes of communication between two processors have already been developed, which are in particular aimed at reducing the transmission errors. Each of these modes is more specifically adapted to a particular type of communication interface. Most of them comply with the HDLC norm (“High-level Data Link Control” established by the International Standard Organization in 1976 (see for example ISO/IEC 13239-1997)), or are derived from this standard by introducing simplified or complementary procedures adapted to particular types of communication interface. Each mode of communication thus designed employs certain frame types defined by the HDLC standard, assigning them specifically to specified categories of messages. Among these modes of communication may be cited:    the PPP protocol (“Point-to-Point Protocol”, see for example IETF—Request for Comments 1134) used for modems for linking to a telephone network. The PPP protocol provides in particular for the periodic introduction of null bits so as to avoid confusion between data bits and control bits;    the GSM protocol (“Global System for Mobile communications,” see GSM 07.10 Technical Specification 101 369 V6.3.0 published by the ETSI—March 1999) particularly adapted for carrying out multiplexing of several applications hosted in a mobile communication unit;    the HCI RS232 protocol, known to the person skilled in the art, used for communication between a host processor and at least one application and a radio communication processor that are internal to a Bluetooth™ communication unit. This protocol is used very little on account of its complexity; and finally    the B-ISDN protocol (“Broadband Integrated Services Digital Network,” see ITU-T Recommendation I.365.4—1996) which proposes a correspondence between AAL 5 frames of CPCS type (“Common Part Convergence Sublayer”) and frames of the HDLC standard.
These various modes of communication are poorly adapted for transmission of data between two processors of one and the same radio communication unit. Indeed, they are complex, without such complexity being necessary, and do not afford sufficient security of the data transmitted.
A need accordingly exists for a simple and effective method of securing the data transmitted between two processors of a radio communication unit.